Method of contouring sheet metal



Feb. 15, 1944.

M. WATTER ET AL METHOD OF CONTOURING SHEET METAL Filed June 18. 1941 INVENTORS: Michael Waiter &

Peter Biehl.

Y B CM 57041:

ATTORNEY PatentedFeb. 15, l

UNITED TATES PATENT OFFICE 2,842,026 METHOD OF CONTOURING SHEET DIETAL Michael Watter, Philadelphia, and Peter Biehl, Willow Grove, Pa., aulgnorl to Edward G. Budd Manufacturing Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 1a, 1941, Serial No. 39am 4 Claims. (01.- its-cs) This invention relates to a method of contour.- ing sheet metal, more particularly, sheet metal members of relatively thin gauge.

In contouring thin gauge sheet metal members of hollow channel shape or flanged cross section by previously known methods which entail lon-. gitudinal stretching of the metal at one side and crowding or compressing at the other side, considerable difficulty has been encountered in that such compression in the thinner gauges causes objectionable wrinkling or buckling of the metal.

One of the objects, of the present invention is to provide a newand improved method of contouring thin gauge sheet metal members to curvilinear shape whereby buckling of the metal at the side of lesser curvature is minimized.

Another object is to provide a contourin method for thin gauge sheet metal members by means of which the stress deformation is such.

as to prevent wrinkling or buckling of the metal.

A further object is to provide a contouring method for thin gauge sheet metal members whereby substantially the entire deformation of the. metal occurs as "a result of tensile expansion.

With the above and other objects in view, which will be apparent from the following detailed description to those skilled in the art, to which the present invention appertains, the present invention consists of certain steps and combination of steps in the method to be hereinafterdescribed with reference to the accompanying drawing, and then claimed.

In the drawing: 7

Figure 1 is a perspective view of a channel shaped member to be contoured to curvilinear shape;

Figure 2 is a side elevation of the channel member shown in Figure l, a portion of the same being shown in section to illustrate elements associated therewith for performing the contouring operation;

Figure 3 is a side elevation of the channel member showing the same in its curvilinear shape;

Figure 4 is an enlarged fragmentary side elevation of the channel member shown in Figure 3, and more clearly showing the elements employed during the contouring operation; and

Figures 5 and 6 are views of one form of the apparatus that may be employed during the contouring operation, the forming rollers thereof being diagrammatically illustrated.

In the accompanying drawing in which like numerals refer to like parts throughout the several views, there is shown, for the purpose of illustrationja C-shaped channel member ID of sheet metal, such as employed as a chord member or cap strip in an aircraft wing structure, which member is to be contoured to the curvilinear shape shown in Figure 3. The channel member ill is provided with a base It and side flanges l2, which terminate in inwardly extending marginal flanges l3.

Various well-known machines have been em- 1 ployed in the past for contouring sheet metal but in each case the underlying principle employed has been one of compressing the vouter metal fibres along the edge of smaller radius of curvature while stretching the outer metal fibres along the other edge in such manner that the fibres took a permanent set. This is the well-known stress distribution of a bent beam.

If, for example, the channel member of Fi ure 1 were contoured to the shape shown in Figure 3 bysuch prior method or principle, the metal of the base It would be tensile stressed and that of the flanges l3 compression stressed. Such methods are fairly satisfactory for use in connection with heavy gauge metal members but in the use of thin gauge metals such as, for example, metals of from .006 to .030 inch in thickness, which are commonly employed in the fabrication of structural members for aircraft, the compression stresses cause the metal, such as that of the flanges l3,.to objectionably buckle or wrinkle.

The present invention contemplates the prevention of the formation of such wrinkles or buckles by a contouring method, wherein in the broad aspect of the invention, the metal fibres are at no time stressed in compression. In broad terms the deformation of the metal during contouring is obtained solely as a result of tensile stress.

In contouring a channel member, such as channel Ill, in accordance with the present invention the member is first conditioned for the contouring operation By closing the channel thereof with a plurality of narrow block-like elements M, each having a flat bottom l5 and an arcuate top It. These elements are of solid non-compressible material arid are disposed in firm abutting relationwith the bottoms lfithereof -to securely hold the block-like elements ll in firm abutting relation to restrain the bases l5 thereof 7 against movement longitudinally of the channel flanges l3 during the contouring operation. The thickness of the block-like elements depends, of

course, upon the degree of curvature to be imparted to the channel member.

The conditioned channel member is then sub- Jected to treatment inthe desired contouring apparatus which shapes it to the desired curvilinear shape, such as shown in Figure 3. During treatment in the contouring apparatus, the forces, which in previously known contouring methods, would tend to compress the metal oi the flanges II and the adjacent metal of the flanges it, are taken by the bases oi the blocklike elements ll, which separate in fan-like fashion as shown in Figures 3 and 4. The deformation of the metal of the channel member as a result of the application of the compression stresses to the block-like elements It occurs through the application of tensile stresses in gradually increasing increments from the flanges l3 to the base l5.

Inasmuch as the metal of the flanges l8 and the adjacent metal of the flanges I2 is not subjected to compressive stresses, it is readily seen that no stresses are exerted which might tend to buckle or wrinkle the metal at the surface of lesser curvature.

In Figures 5 and 6 the channel member is shown in the process of being contoured in a roller forming apparatus, the rollers l8 thereof being diagrammatically shown.

The invention is not confined to practice in the use of any particular apparatus inasmuch as it can be practiced with roller forming machines, bending machines or any other standard machine normally used for contouring.

After the contouring operation, the ends of the channel member containing the rigid members I! can be removed in any suitable manner s ch as, for example, by sawing, after which the block-like elements i4 may be removed, or by removing the bolts or rivets when bolts or rivets are employed as the securing means for members ll.

It is seen in the practice of the present invention that by reason of the abutting engagement of the base l5 of the block-like elements N that such bases upon the application of bending stresses to the opposite longitudinally extending transverse surfaces of the channel member 10 prevent the application of compressive stresses to the metal adjacent the bases I5, with the result that the entire deformation to length of said member, and bending said beam with the blocks retained therein while prevent- ,ing elongation of said beam along its portion curvilinear contour takes place through the application of tensile stresses. In other words,

the metal which in prior methods is subjected toconipressive stresses during the vending operation is, in the present invention, maintained substantially in unstressed condition.

While the present invention is described and illustrated in connection with a channel section having inturned marginal flanges, it is obvious that the invention is as equally adaptable to channel members having outturned or no marginal flanges and to L-shaped structural elements wherein in each instance means is provided to prevent the metal adjacent the surface which assumes the lesser contour from being subjected to longitudinal compressive stresses, whereby wrinkling or buckling is prevented.

The term non-compressible where used in the specification and claims is to be interpreted in the sense that the elements ll are more reof lesser radius, whereby the inner ends or bases of said blocks are placed in compression and the walls of said beam outward of the bases of said blocks are stretched in tension.

2. The method 01 bending a hollow thinwalled beam to prevent buckling, which comprises, reinforcing the beam by a plurality of contour-fitting compression blocks, securing said blocks against separation at one edge on the compression side of short radius during bending, and bending the block-reinforced beam, with the compression side disposed at the short radius while preventing elongation of the beam and separation of theblocks on the compression side,

whereby the inner ends of said blocks absorb,

most of the bending compression and the beam walls outward of the inner ends of the blocks are elongated in tension while supported by the blocks.

3. The method of bending without buckling a hollow non-circular thin-walled beam, such as a hollow rectangular sheet metal beam having an opening along one side, which beam buckles easily on the compression side of short radius when bent on the normal neutral axis of intermediate radius, the method comprising, reinforcing the beam by a plurality of contour-engaging compression blocks which engage each other on the compression side and securing the blocks against separation on that side whereby to shift the neutral axis temporarily to the compression side, and bending the reinforced beam about the temporary neutral axis with the compression side on the short radius, whereby to elongate the walls beyond the temporary neutral axis while said walls are supported by the blocks and thus preventing buckling and other unauthorized distortion during bending.

4. The method of bending without buckling a,

hollow rectangular thin-walled sheet metal beam, which comprises, placing within said beam a plurality of separate rectangular contour-fitting compression blocks having rounded outer edges curved in the direction of bending, securing said blocks against separation at one edge on the compression side of short radius during bending, and bending the block-reinforced beam with the compression side disposed at the short radius while preventing elongation of the beam and separation of the blocks on the compression side, whereby the inner ends of said blocks absorb most oi the bending compression and the beam walls outward of the inner ends of the blocks are elongated in tension while supported by the blocks.

MICHAEL WA'I'I'ER.

PETER BIEHL. 

